1. Field of the Invention
The present invention relates to a detecting and protecting device of a shrink film machine, more particularly one, which includes a sensor, and a shading block normally shading the sensor; the shading block will be displaced, and no longer shade the sensor if the bag expanding device comes into contact with the goods during downward movement thereof owing to incorrect position of the goods.
2. Brief Description of the Prior Art
Referring to FIG. 11, a currently available shrink film machine includes a frame 1, a bag feeding device 2, a bag sealing device 3, a bag sucking device 4, and a bag expanding device 5. The bag feeding device 2 is used for feeding continuous bags. The bag sucking device 4 has a sucking unit, which will suck an opening end of the bag, and which will move so as to open the bag after the opening end has been opened. The bag expanding device 5 has several supporting rods 51. The bag will be positioned around the supporting rods 51 after the bag is completely opened. Next, the supporting rods 51 are moved such that the bag is further expanded to the largest size possible. And, an up and down movable support for the supporting rods 51 moves downwards with the supporting rods 51 gradually releasing the bag so that the bag is wrapped around a pallet and goods on the pallet.
The inventor of the present invention develops an improvement on a cold shrink film wrapping machine, which includes a frame, a bag feeding device, a bag sealing device, a bag sucking device, and a bag expanding device. The bag feeding device and the bag sealing device are positioned on top of the frame, and are respectively used for feeding continuous bags, and for sealing and cutting the bags. A conveying mechanism is positioned right under and across the frame for conveying a pallet and goods on the pallet through the frame.
The bag sucking device includes left and right bag-sucking assemblies, which have the same structure, each having first and second air-sucking units positioned around respective ones of two opposed slide rods. Each of the slide rods of the left and the right bag-sucking assemblies are connected to pulley assemblies at two ends such that they are supported on guide rods of the upper end of the frame. Tail ends of the slide rods of the right bag-sucking assembly are securely joined to a first end of an output shaft of an air cylinder, which is secured on the frame. And, the left and the right bag-sucking assemblies are connected to chains such that they can be moved away from each other, and they can be moved closer to each other. Furthermore, each of the air-sucking units has an air cylinder of an air cylinder assembly securely connected to a rear end thereof; the air cylinder has a swing arm pivoted to the other end of an output shaft thereof, which swing arm is pivoted to the air-sucking unit at one end, and securely connected to a pressing rod at the other end thereof; thus, when the air cylinder is working, it will make the pressing rod swing inwards.
The bag expanding device includes up and down movable supports, a first left, a second left, a first right, and a second right bag expanding assemblies, which are connected to respective ones of the up and down movable supports; each of the up and down movable supports has a sliding base, which is supported on a rail of the frame of the machine; the up and down movable supports are connected to a power source by means of respective up and down movable chains such that when the power source is activated, each of the up and down movable supports and the respective bag expanding assembly will be moved together. In addition, each of the first left, the second left, the first right, and the second right bag expanding assemblies includes a base, an extension arm, and a bag collecting unit; the bases are secured on respective ones of the up and down movable supports; each of the bases has a motor secured on a lateral side thereof such that the extension arm can be stretched and withdrawn by means of activating the motors; each of the extension arms has an upright support board secured to the other end thereof, which has a through hole on a middle portion, and a rolling shaft held in the through hole thereof. Furthermore, the bag collecting units are respectively positioned on upper ends of the bases, and they each have an air cylinder secured on the corresponding base; each of the cylinders is securely connected to a bag-collecting motor at the other end thereof; each of output shafts of the bag-collecting motors is securely connected to a pressing wheel. Thus, when the air cylinders work to make the bag collecting motors move outside, the pressing wheels will be pressed against the rolling shafts of the upright support boards of the extension arms.
Therefore, after packaging bags are fed, the air-sucking units of the bag-sucking device will suck the packaging bags. After the pressing rods of the air cylinder assembly will be pressed against corners of the packaging bags to make them stay in position, the bags will be completely expanded without the risk of falling off. The bag expanding device will feed a certain length of packaging bag, and the bag will be collected under the support boards by means of the pressing wheels of the bag collecting units. When the extension arms are withdrawn, the bags will be expanded to the largest size possible such that the bags will be positioned around the goods and the pallet when the bag-expanding device is lowered.
The above mentioned shrink film machines have the following disadvantages: Because the shrink film machines aren't equipped with any detector, if the goods are tilted or improperly positioned, the bag expanding assemblies will hit the goods, causing damage to themselves and the goods. And, the shrink film machines aren't equipped with any sensor for measuring the height of the goods.